Electron beam convergence apparatus



March 31, 1959 M. KOLESNIK ETAL 2,880,364

' ELECTRON BEAM CONVERGENCE APPARATUS Filed Feb. 15, 1956 i :5 Sheets-Sheet 1 W n/ram JWIQMM $601270 B Y March 31, 1959 M. KOLESNIK ET AL 2,880,364

ELECTRON BEAM CONVERGENCE APPARATUS Filed Feb. 15. 1956 I s Sheets-Sheet 2 4/ 44 aw 40 KN g ELECTRON BEAM CONVERGENCE APPARATU Michael Kolesnik, Haddon Heights, and Gordon E. Kelly, Haddonfield, N .J., assignors to Radio Corporation of America, a corporation of Delaware Application February 15, 1956, Serial No. 565,616

' 8 Claims. (Cl. 31522) The present invention relates to apparatus for controlling the electron beams of a cathode ray tube and, particularly, to a system in which a plurality of electron beams is deflected by a common deflection apparatus.

One type of cathode ray tube with which the present invention may be successfully employed is a color kinescope of the general type described in an article entitled Development of a 21" Metal-Envelope Color Kinescope, by Seelen et al. published in the RCA Review for March 1955, at page 122. Such a tube has a luminescent screen as part of a target electrode structure and in which different phosphor areas produce difierently colored light when excited by electron beam components impinging upon the target structure from different angles, the angle of impingement determining the particular color of the light produced by the phosphor areas.

It is necessary for the satisfactory operation of such kinescopes to eifect substantial convergence of the different electron beams at all points of the raster scanned thereby at the target electrode structure. In general, the matter of beam convergence is discussed in an article entitled Deflection and Convergence in Color Kinescopes, by A. W. Friend, Proceedings of the IRE, Octoher 1951, at page 1249. One type of apparatus for controlling the convergence of a plurality of electron beams at a target electrode structure and with which the present invention is particularly concerned comprises, in general, individual electromagnetic means located respectively adjacent to the predeflection paths of the respec tive beams and of such character as to be energizable from the beam deflection circuits in a manner to effect the desired beam convergence.

2,880,364 Patented Mar. 31, 1959 2 netic coils wound about magnetic core means associated with the internally located pole pieces of the kinescope. That is, the vertical frequency convergence .waveform is applied to one winding of each of the individual elec ice ' tro-magnets, while the horizontal frequency waveform is applied to a second winding of each of the electro-magnets. In accordance with one aspectof the invention, the location of the vertical and horizontal frequency convergence windings with respect to each other afiords improved convergence of the electron beams.

In accordance with another aspect of .the invention, static convergence of the electron beams is efiected by the applicationof suitable direct currentenergy to one of the electromagnetic windings of the convergence magnets. r

As will be appreciated, the convergence apparatus .of

the. present invention provides increased sensitivity "and The particular beam convergence electromagnetic y means to which this invention pertains includes, for each beam, a pair of pole pieces located internally of the kinescope envelope. The internally located pole pieces are energized by magnetic apparatus located externally of the kinescope and associated, respectively, with the different pairs of pole pieces. require, in general, energization both statically and dynamically, the latter energization being in accordance with a function of the angles through which the electron beams are deflected.

The convergence pole pieces It is, therefore, an object of the invention to provide convergence magnets of a tri-color kinescope are energized by vwaves which are readily available in both the vertical and horizontal deflection circuits which produce the scanning deflection of the beams. These waves are suitably shaped and applied, respectively, to electromag at lower cost than that of certain prior art arrangements.

Additional objects and advantages of the present invention will become apparent to those skilled in the art from a study of the following detailed description of the accompanying drawing, in which:

Figure 1 illustrates a cathode ray tube convergence system embodying one form of the present invention;

Figure 2 is a vertical sectional view taken along line 2--2 of Figure 1; and

Figures 3 and 4 are schematic diagrams of circuits for energizing the convergence magnets of Figures 1 and 2.

Reference will first be made to Figure 1 of the drawing for a general description of an illustrative embodiment of an electron beam convergence system in accordance with the presentinvention. The system includes a tri-color kinescope 11 which may be of the same general type as that disclosed in the Seelen et al. article referred to above. The kinescope has a luminescent screen 12 provided with a multiplicity of small phosphor areas arranged in groups, the areas of each group being capable respectively of producing light of difierent component colors in which the image is to be reproduced in response to electron impingement. In back of and spaced from the screen 12 is an apertured masking electrode 13 having an aperture for and in substantial alignment with each group of phosphor areas of the screen 12. It will be noted that both the luminescent screen and the masking electrode have generally spherical surfaces which are substantially concentric. .It is to be understood, however, that the present invention is equally 'applicable to other forms of target electrode configuration. In the particular case illustrated, the kinescope also has a plurality of electron guns, equal in number to the number of component colors in which the image is to be reproduced. Each of these guns may be conventional, consisting of a cathode, a control grid and a focussing electrode. Since the three guns are identical, the diflferent parts thereof will be referred to collectively as the cathodes 14, the control grids 15, and the focussing electrodes 16. The three electron guns produce schematically represented electron beams 17, 18 and 19 by which to energize, respectively, the blue, red and green phosphor areas of the screen 12. When these electron beams are properly converged at the target electrode structure in cluding the screen 12 and the masking electrode 13, they pass through the apertures of the masking electrode from different directions and impinge upon different phosphor areas of the various groups so as to produce blue,fred and green light. It is to be noted that the size of the phosphor areas, the angles between'the beams and the spacing of the mask 13 from the screen 12 as compared with the length of the tube are exaggerated for better illustration of this aspect of the kinescope.

The electron-optical apparatus of the kinescope 11 also includes a beam-accelerating electrode consisting, in the the cosmetic present instance;of-='a=conductivewall coating 20 termed on the inner surface of the tubular glass neck 21 and conical section 22 of the "kinescope extending from the region; adja cent to the-outer-.-end' of the -focussing electrodes 16 to the target electrode-region. Preferablyflhe targetelectrode structure, including the masking electrode "13' and the luminescent screen '12, which for-this purpose may be metallized, is electrically connected to the wall coating. '20 by suitable conventional means (not shown). Metallization of a luminescent screen of the character described may be eflecte'd -in'the' manner disclosed in a paper by D. W. Epstein i and L. Pensak entitled improved .Cathode' Ray Tubes with-Meta1 Backed-Luminesg-cent screens, published in"th e RCA Review, vol. *VII, ;M=%r 946 a ra s- :19-

:Ih slsssribsdsls trcrest ict n n -flr t'ki swpe m y be energized in a conventional manner such-:as" that illushated. Ihe source 91 en e 1; gy. i s represented by a battery ross the ninals of Whichthere is connected a yoltage fdividerpif The 'jca'thodes more connected to ,the grounded point qfithe voltage {divider and-the control grids 15 are connected to a point which is somewhat negative relativeto "ground. "Similarly, the focussing electrodes 16 are connectedto apoint on the voltage divider which may conventionally be at a potential of approximately 4,060 volts positive relative to the grounded cathodes. Also, the 'beam accelerating anode, including the wall coating 20, is'connectedto the-voltage divider 24 at a point which may conventionally be approximately 27;00O"volts posit ive relative to the grounded cathodes.

The electron beams .17, 18 and '19are modulated suitably in intensity under the control of 'color-representative video signals derived from a source 25. It will be understood that the video ,signal source is represented gherein entirely diagrammatically since it does not per se form part of the present invention. The signal source 25 usually will'be .part of a signal receiver and may be understood to include a signal detector, 'or equivalent device, together with one or morestages of video signal amplification. Alternatively, the video signal source'may be a color television camera in the event that the kinescope 11 is employed as amonitor, 'for example. Also, it .will be understood that the illustrated connection of the video signal source 25 to the electron guns of the kinescope 11 is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes 14. Instead, it will be understood, that they ma he r a's w t e ds 115 i 'a da e i Qther rnodes (if operation of colorimage-reproducing apparatus,

the yideo signal source may be connected both to the cathodes and to the control grids of the ;clect ron guns.

;Al so "associated with the .jcoior'kinescope 11 is a deflection yoke '26 which may "be entirely conventional including two pairs of suitably placed coils electrically connected together in such a manner that, when properly energized, electromagnetic fields are produced, whereby to eflect both horizontal and vertical angular deflections of the electron'beams so as to scan the usual rectangular raster at the target electrode structure. Energization of the deflection coils comprising the yoke 26 may be effected by conventional vertical and horizontal deflection wave generators 27 and 28, respectively. Such apparatus will he understood to function suitably to produce substantially sawtooth wave energy at both horizontal and s is defle t n frequenc s @tha h fi d Pr u the Yes? 6 ar i d n a su st n l s o 11 1 .9

Thsbs m s r r sncssvstsm n s danc wi h t present 'inyention, a lso includes .a plurality of electroma et field-Prod n e em t s h as the t magnets 29, '30 and (see also Figure '2) mounted around the neck 21 of the color kinescope adjacent to sd fiscticn P ths o t e e c ro b amsis be understood that the precise location of these magnets ..is-.not.necessarily .indicatedinFigure 1. .Instead, it,is to be understood that each of these magnets is located relative to one of the electron beams so as to influence its associated beam to the virtual exclusion of the others. Furthermore, it is to be understood that these magnets are of a character which, when suitably energized, produce respective fields which are transverse to the asso ciated beam paths and in directions .to move the associated beams radially relative to the longitudinal axis of the kinescope 11.

Each of these convergence .electromagnets includes a generally U-shaped pole piece or core member and a pair of energizing-windings. "Two-windings are provided for each of the electromagnets for separate energization, as will be described subsequently in' greater detail.

Before describing the details of the particular beam convergence system in accordance with the present inwention, a brief .description willbe givenof the general manner in which the apparatus functionstogproducethe desired-results. The convergencetmagnets 29, 30 and-31 structure including thescreen 12-and the apertured masking electrode 13. In orderto do this, .the unidirectional energization of these magnets is effected in such a way that the magnets maybe individually energized in different magnitudes. In eflecting this initial beam convergence, it is to be understood thatthe beams may be in any desired one of their different udeflected positions. For examplethey may 'beinitially' converged atthe center ot'the raster to be scanned. Alternatively, they may be initially converged at one corner of .the raster.

The convergence magnets-29,30 and '31 also are dynamically energized by the control wave energy derived from suitable generators (shown-in, and described subsequently with reference to, Figures 3 and 4) so as to effect a variation in themagnitude of the transverse fields produced respectively thereby. These field strength variations are in accordance with a predetermined function (usually approximately parabolic) of the angular beam deflection. Variations in the strength of the fields produced by the convergence magnets effect corresponding variations in the paths of the electron beam components relative to the longitudinal axis of the tube. Hence, suitable'variations aremade in the convergence angles between 'the'various beam components so as toproduce the desired convergence of the beam components sub- .stantially at the target electrode structure including the screen 12 and the masking electrode 13.

For a further description of this type of beam convergence apparatus, reference now will be made to Figure 2 'of the drawings. "This figure shows more clearly the positions of the convergence magnets 29, 30 and 31 relative to one another and to the electron beams-withwhich they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of them will be described in detail. The convergence magnet 29, which is associated with-the blue electron beam 17, is provided with a core having two'external pole pieces which are mounted so as to be in close association with the tube neck 21. The magnets may be mounted around the neck of the kinescope byany suitable means such as holders of insulating material which are spring-urged together. The magnet also is provided with an energizing structure.

In Figure 2, it also is illustrated that for each of the convergence magnets there are provided on the inside of the tube neck 21 internal pole pieces so as to increase the eflectiveness of these magnets. 'The magnet 29, for example, is provided with a pair of inwardly extending internal pole pieces 37 and 38, associated respectively with the external pole pieces. By such means, the reluctance of the magnetic circuit is considerably decreased, and also the flux distribution-of the field p'roducedbetween theinterna-l pole .pieces .37 and 38 is. considerably improved;

Thus, the convergence magnet 29 effectively produces a field which, in the vicinity of the electron beam 17,

is substantially transverse to the axis of the kinescope.

tively control the electron beams 18 and 19 in a substantially similar manner.

The magnet 29 comprises a generally U-shaped pole piece 40 of ferrite or other suitable magnetic core material-, the extremities of the legs of the U being located adjacentto the internally located pole pieces 37 and 38. p Electromagnetic coils 41 and 42 for energizing the magnet 29 with a suitable waveform of television vertical or field frequency are wound about the legs of the U near the bight thereof (i.e., remote from the extremities of the legs of the U). Electromagnetic coils 43 and 44 are also wound about the legs of the U-shaped pole piece 40 adjacent their extremities. These latter coils are adapted for energization with horizontal deflection frequency energy of suitable wave shape. be seen that the magnet 30 comprises a U-shaped core member vertical frequency exciter coils 41' and 42' and horizontal frequency exciter coils 43 and 44'. Similarly, the magnet 31 includes a U-shaped pole piece 40", vertical exciter coils 41" and 42" and horizontal exciter coils 43" and 44".

- Circuitry for energizing the horizontal frequency excitercoils of the magnets 29, 30 and 31 is illustrated in Figure3 of the drawing wherein reference numerals identical to those employed in Figure 2 designate the same parts. A positive-going pulse 45 of generally rectangular wave shape is applied to the input terminal 46 of the horizontal convergence circuitry. Pulses such as the one represented by reference numeral 45 may be derived by connecting the terminal 46 directly to a suitable pointin the horizontal deflection wave generator 28 such, for example, as the usual horizontal output transformer found in conventional television receivers. The pulse 45 may be of volts amplitude, peak to peak,

and is integrated by the variable inductance 47 into a generally sawtooth wave shape 48 connected to the input terminal 46. A shunt path comprising a capacitor 49 and the parallel combination of a variable inductance 50 and resistor 51 serves to shape the wave form 48 further toward a parabolic voltage wave form as indicated at 52. This wave form, when passed through the coils 43 and 44, connected in series aiding relationship, produces a generally parabolic current waveform 53 in the coils for producing the required parabolically varying magnetic field between the pole pieces 37 and 38 of the kinescope. form flowing through the coils 43 and 44 is controlled by the variable series inductance 47, while its tilt (i.e., shift in the minimum amplitude point of the parabolic wave toward the beginning or end of the wave) is con-.

trolled by the variable inductance 50. It is to be noted that the waveshaping function is performed, in part, by

r the inductance of the coils 43, which aids in integrating frequency. exciter coils such as the coils 41 and 42 of the magnet 29. In Figure 4, there is shown av conven- It will further The amplitude of the convergence wave-' tional vertical deflection output stage includinga vertical deflection wave amplifier54 whose anode 55 is connected to one end of the primary winding 56 of a deflection output transformer 57. The other end of the primary winding 56 is connected through a suitable resistor 58 to a source of positive operating potential indicated at the terminal 59. The screen grid electrode 60 of the amplifier 54 is connected to the upper end of the resistor 58 and is bypassed for signal frequency by a capacitor 61. The suppressor grid electrode of the amplifier is conventionally connected to the cathode 62 which, in turn, is connected to a point of reference potential (e.g., ground) through a small biasing resistor 63. The amplifier 54 is adapted to receive at its control grid input terminal 64 a conventional spiked sawtooth, voltage wave of the vertical deflection frequency from a suitable source such asthe usual vertical deflection oscillator. The transformer 57 includes a secondary winding 65 connected to the vertical deflection coils of the yoke 26 in a conventional manner for applying vertical deflection frequency energy to the latter.

As described thus far, the vertical deflection amplifier 54 and its associated circuitryare in accordance with conventional practice. Energization of the vertical frequency exciter coils of the convergence magnets (also shown in Figure 4) is effected in the following manner:

A sawtooth voltage wave shaped generally as indicated by the waveform 66 is derived from the cathode 62 of the vertical deflection output amplifier 54. This voltage wave, peaked somewhat as shown, is applied across a plurality of otentiometers 67, 68 and 69 via a lead 70 to furnish, ultimately, a parabolic current wave through the vertical frequency exciter coils such as the coils 41 and 42 of the magnet 29. Thus, a controllable amount of the voltage wave 66 appearing across the potentiometer 67 is applied via the adjustable tap 71 to one end of the coil 42, as illustrated. A winding 72 on the transformer 57 has induced therein a voltage wave such as that indicated at 73, which voltage wave is in the nature of a peaked sawtooth wave for controlling the tilt of the parabolic current waveform to be produced in the coils 41 and 42 of the magnet 29. The amplitude of the tilt voltage applied to those coils is controlled by the potentiometer 74 whose movable contact 75 is connected to the coil 41 of the magnet. Thus, by adjustment of the tap 71 and the contact 75 of the potentiometers 67 and 74, the amplitude and tilt of the voltage waveform applied to the coils 41 and 42 may be controlled. The voltage composite waveform resulting from the combination of the waves 66 and 73 is integrated by the inductance of the coils 41 and 42 to produce therein the generally parabolic current wave 76.

In accordance with a further aspect of the present invention, static convergence of the beams 17, 18 and 19 is effected through direct current energization of the magnets 29, 30 and 31, rather than through the use of auxiliary permanent magnets as in certain prior art arrangements. Specifically, the present invention provides means for applying variable direct current energy to the vertical frequency exciter coils of the convergence magnets. Thus, Figure 4 further illustrates a plurality of parallel, center-tapped potentiometers 77, 78 and 79 connected between a source of positive voltage at the terminal 80 and a point of reference potential, such as ground. Associated with the potentiometer 77 is a slider tap 81 which is connected to one end 82 of the vertical blue tilt controlling potentiometer 74. It will, therefore, be understood that positioning of the slider tap 81 on one side or the other of the center tap 83 of the potentiometer 77 will cause a reversible direct current to flow through the coils 41 and 42 via the tap 75 or the potentiometer 74.

' Thus, the current waveform 76 will be superimposed upon anemone 7 titer .coilsiof Joe-smegma 30 n.d.3 1 are similar toith described in connection with the magnet 29. The pri mary difference, however, istthat while the-tilt waveform .73 provided by the winding72 for application to the coils 41 and 42 is adjustable'gonly as to magnitude, for reasons of simplicity, the tilt waveforms provided by the wind ings 85 and 86,for use in the magnets 30 and 3l are adjustable both as to amplitude and polarity. That is to say, .the winding 85 on the transformer 57 is centertapped, the center tap 87 being connected to the slider tap 88 on the potentiometer 78 which controls the application of static convergence current to the coils 41 and 42. Thus, there appear at opposite ends of the verti a red tilt control ing p tentiomet r "op ositely polarized waveforms 90 and Y91 corresponding in wave i shape to the waveform 73 appearing across the poten- "tiometer 74. Ihe'centertap of the transformer winding 8'6 is similarly connected to theislider gtap I011 the ,potentiometer 79.

- current being controlled by the tap 88 with respect to the center of the potentiometer 78. Simultaneously, a peaked sawtooth wave for controlling tilt is available at the tap on the potentiometer 89, the amplitude and polarity of this latter waveform being controlled by adjustment of the potentiometer 89, so that the degree and direction of the tilt of the parabolic currentwave produced in the coils '41 and 42 are adjustable. Thus, a parabolic current waveform resulting from the integration effect of the coils 41 and 42 and a direct current of controllable amplitude and direction flow through the vertical frequency exciter coils of the magnet 30. Energization of the exciter coils 41 and 42" of the magnet 31 is effected in substantially the same manner as that described in connection with the magnet 30.

Before describing in detail the overall operation of the convergence circuits of Figures 3 and 4 in cooperation with the magnets shown in Figure 2, note will be made of a further element of the present convergence'system, namely, the apparatus for controlling initially thep osi- *tioning of the blue-designated electron beam 17. As'set forth in an article by J. Obert, entitled Deflection and Convergence of the 21-inch ColorKinescope, which appeared in the same issue of the RCA Revie'was the Seelen et al. article, it is conventional to provide means for initially and statically positioning one of'the beams (e.g., the blue beam) laterally so that all three 'beams' with the tube for producing lateral shifting of the beam 17 when energized by suitable direct current. This energization is afforded by the circuitry of Figure 4 which in cludes a potentiometer 100 in parallel with the static convergence potentiometers '77, 78 and 79. 'Theelectro' magnetic winding of the magnet 99 is connected to the potentiometer, as shown, in such manner that a'direct'cur- "rent of reversible direction and variable amplitude be caused to flow through the winding. Sincethe'mag- "net 99 does not per se form a part of the present inven- "t'ion, it need not be described further herein.

It has been found that the arrangement of the'Ivertical and'liorizontal frequency'convergence windings on the U shape'd core pieces affords, as mentioned above, afdistinct advantage in operation. As will be understoodrfrom the circuits of "Figures ,3 and "4,ithe impedance across the vertical convergence windingssuch as the-windings 41 and'42 ,of the magnet 29 :is :low. That is to say, the impedance across "the vertical convergence windings is essentially the parallel combination of the potentiometers enumerated above. By reason of the low impedance across the vertical convergence windings, the vertical windings appear somewhat as a short-circuited turn to the horizontal frequency convergence windings with which they are respectively associated. Stated otherwise, ifthe horizontal and vertical frequency convergence windings .of one of the convergence magnets are viewed, respectively, as the primary and secondary windings of the transformer, the low impedance of the secondary winding --will appear as a low impedance to 'the'primary winding, thereby lowering the inductance of the primary winding. Moreover, the low impedance of the vertical frequency 'convergence'windings has an effect upon the pole mem- "ber--40which is akin-to saturation-of the pole piece or core. This results in increased sensitivity of the horizontal frequency convergence windings, since the flux produced thereby is channelled directlyinto the internally located pole pieces of the kinescope'rather than being circulated through the ferrite core. 'The sensitivityof the horizontal frequency convergence windings is furtherincreased over prior arrangements by reason of the fact that the horizontal windings are, inaccordance with the present invention, located physically close to the neck of the kinescope.

On the other hand, the horizontal frequency convergence windings have associated therewith a relatively high impedance compared to that of the .vertical frequency windings, so that the horizontal frequency wind- .ings do not have any appreciable loading effect upon the vertical windings and do not appreciably affect the passage of the vertical frequency fiux through the legs of the .U-shaped core into the kinescope neck. It will, therefore, be understood that the convergence magnets such as the magnet 29 act as a flux-switch, :in that the horizontal frequency convergence flux is channelled directly into the kinescope neck, while the vertical frequency flux is permitted to pass normally through the core member into the internally located pole pieces of the kinescope. The operation of the present apparatus -may be contrasted with certain prior art arrangements which have been found to provide appreciably lower transferenceofcurrentenergy into magnetic flux. -Moreover, the present apparatus is not subject to any appreciable amount of undesirable interaction between the horizontaland vertical frequency convergence windings. To .preventundesirable interaction between the vertical and horizontal windings through their energizing circuits,

there :is provided a .filter network comprising the series combination of an inductance 101 and capacitor 102 connected in shunt with the lead 70 which supplies the convergence voltage waveform to the convergence amplitude potentiometers. This filter network serves to prevent feedback of horizontal frequency energy to the vertical deflection amplifier circuits. It will be noted that the circuitry of Figures 3 and 4.does not include any isolation chokes, since the need for such devices is substantially obviated by the present invention.

In the interest of completeness .of description and by .way .of illustration, it may he noted that the vertical frequency windings of the magnets 29, 30 and 31 comprise 1400 turns each, having an inductance of 150 mh. at l-kc., while the horizontal frequency winding associated'with the blue convergence magnet 29 comprises turns, the corresponding horizontal windings .of the magnets 30 and 31 having turns each. The inductance of the windings 43, 44 is 0.23 mh. measured with the vertical frequency coils short circuited, while the windings 43, '44 and 43", 44" have an inductance of 0.39 mh.

,l-laving thus described opr invention, what we claim as .a raster at -a target electrode structure, the combination comprising: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including a first and a second winding; means coupled to said beam deflection apparatus and to the first winding of at least one of said electromagnets for causing a current wave of vertical deflecting frequency to flow through said first winding; and means coupled to said beam deflection apparatus and to the second winding of at least one of said electromagnets for causing a current wave of horizontal deflection frequency to flow through said second winding.

2. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse pre-deflection paths spaced respectively about the longitudinal axis of the tube, are angularly deflected by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination comprising: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including a first and second winding; means coupled to said beam deflection apparatus and to the first winding of at least one of said electromagnets for causing a current wave of vertical deflecting frequency to flow through said first winding; means coupled to said beam deflection apparatus and to the second winding of at least one of said electromagnets for causing a current wave of horizontal deflection frequency to flow through said second winding; and means for causing direct current to flow through one of said windings of at least said one electromagnet.

3. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse pre-deflection paths spaced respectively about the longitudinal axis of the tube, are angularly deflected by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination comprising: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including a first and a second winding; means coupled to said beam deflection apparatus and to the first winding of at least one of said electromagnets for causing a current wave of vertical deflecting frequency to flow through said first winding; means coupled to said beam deflection apparatus and to the second winding of at least one of said electromagnets for causing a current wave of horizontal deflection frequency to flow through said second winding; and means for causing direct current to flow through said first winding of at least said one electro magnet.

4. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse predeflection paths spaced respectively about the longitudinal axis of the tube, are angularly deflected by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination comprising: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including U-shaped magnetic core means and a first and a second winding on said core means; means coupled to said beam deflection apparatus and to the first winding of at least one of said electromagnets for causing a current wave of vertical deflecting frequency to flow through said first winding; and means coupled to said beam deflection apparatus and to the second winding of at least one of .said eleetromagnets forcausingacurrent wave of hen- 'zontal deflection winding.

frequency KOflOWfihIOUgh said second 5. In a cathode ray tube image reproducing'system wherein a plurality of electron beam components, which traverse predeflection paths spaced respectively about the longitudinal axis of the tube, are angularly deflected by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination comprising: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including U-shaped magnetic core means having a pair of legs extending toward such tube, a first winding on said legs remote from their extremities, a second winding on said legs nearer their extremities; means coupled to said beam deflection apparatus and to the first winding of at least one of said electromagnets for causing a current wave of vertical deflecting frequency to flow through said first winding; and means coupled to said beam deflection apparatus and to the second winding of at least said one electromagnet for causing a current wave of horizontal deflection frequency to flow through said second winding.

6. In a cathode ray tube image reproducing system wherein a plurality of electron beam components, which traverse predeflection paths spaced respectively about the longitudinal axis of the tube, are angularly deflected by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination comprising: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including U-shaped magnetic core means having a pair legs extending toward such tube, a first winding on said legs remote from their extremities, a second winding on said legs nearer their extremities; means coupled to said beam deflection apparatus and to the first winding of at least one of said electromagnets for causing a current wave of vertical deflecting frequency to flow through said first winding; and means coupled to said beam deflection apparatus and to the second winding of at least said one electromagnet for causing a current wave of horizontal deflection frequency to flow through said second winding, said means for causing a current wave of vertical deflecting frequency to flow through said first winding presenting a relatively low impedance to said first winding.

7. In combination with a cathode ray tube imagereproducing system wherein a plurality of electron beam components, which traverse predeflection paths spaced respectively about the longitudinal axis of the tube, are angularly deflected by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including a first and a second. winding; means coupled to said beam deflection apparatusand to the first winding of at least one of said electromag nets for causing a current wave of vertical deflecting frequency to flow through said first winding; and means coupled to said beam deflection apparatus and to the second winding of at least one of said electromagnets for causing a current wave of horizontal deflection frequency to flow through said second winding.

8. In a cathode ray tube image reproducing system wherein a plurality of electron beam components, which traverse predeflection paths spaced respectively about the longitudinal axis of the tube, are angularly deflected by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination comprising: a plurality of beam convergence electromagnets respectively mounted adjacent to such predeflection paths, each of said electromagnets including U- shaped magnetic core means having a pair of legs extending toward such tube, a first winding on said legs remote from their extremities, a second winding on said legs neat" awe-364 '11 12 er th ir'extremities;- means cou led to said beam 'deflecf forapplyi'n'g directxeurfent energiiation' tb aid first Wind- :tiem apparatusand tothe first-winding of at least one of ing.

said electromagnets for causing a current wave of vertical deflecting frequency "to flow through said first winding; References Cited il'the me of this-P31131t means coupled to said *beam deflection apparatus and to 5 UNITED STATES PATENTS the second winding of *atleast said one electr-omagnet for causing a current wave of horizontal deflection fre- 2,707,243 GOOJ'IiCh c P v1955 

